1. Field of the Invention
The present invention relates to a method for selectively exposing a predetermined area of a peripheral part of a semiconductor wafer used for producing ICs, LSIs and other electronics elements.
2. Description of the Prior Art
In forming a fine pattern in a process for producing ICs, LSIs and the like, it is a conventional practice to apply a photoresist onto a silicon wafer or the like, expose and develop it, thereby forming a resist pattern Then, the resulting photoresist pattern is used as a mask to effect ion implantation, etching, lifting-off and other steps.
Usually, the resist is applied by a spin coating process. The spin coating process involves spinning the wafer while applying a resist onto a central location on a wafer surface so as to distribute the resist over the entire surface by a centrifugal force.
A peripheral part of a wafer is mechanically chucked or held in handling in many processes. And on a peripheral part of a wafer, a pattern tends to be distortedly transfered. So, a peripheral part is not usually utilized in producing elements. But, resist is applyed on the peripheral part the same as the pattern formation part. If the resist is positive type, the resist on a peripheral part may remain after development. In some cases, the peripheral part of the wafer with resist may be chucked or held mechanically and may be rubbed by a wall of a container such as a wafer cassette, resulting in a source of generation of refuse. Particularly under the increase of functional level and integration density, it is a serious problem that an unnecessary resist portion remaining on the peripheral part of the wafer generates refuse to provide a reduced yield.
Thereupon, for removing such an unnecessary resist portion remaining on the peripheral part of the wafer even after development, an approach conventionally practiced is to specially expose the unnecessary resist portion on the peripheral part of the wafer to remove it in a developing step, apart from the exposure for forming the pattern.
FIGS. 10a, 10b, 10c and 10d are schematic diagrams for explaining a prior art method for exposing a peripheral part of a wafer to remove such an unnecessary resist portion.
The wafer 1 is placed onto a rotary stage 2 by means of a transporting system (not shown), and the rotary stage 2 is rotated. An orientation flat 1f of the wafer 1 is detected by a sensor 72, and when the orientation flat 1f has substantially reached a predetermined position, the rotation is stopped. Then, centering and positioning of the orientation flat 1f are conducted by use of an orientation flat pushing plates 74a and pins 74b, and 74c and 74d.
After such positioning, light is illuminated through an emitting end of a fiber lightguide while rotating the wafer 1 to expose circle wise the peripheral part. By the exposure upon this rotating motion (in a direction indicated by an arrow 76a), a peripheral part along the orientation flat 1f is not completely exposed because such exposure is as shown in FIG. 10c. Therefore, it is necessary to further effect an exposure by moving the emitting end 75 in parallel to the orientation flat 1f (in a direction of an arrow 76b), after moving the orientation flat 1f to a predetermined location and stop it thereat.
The above prior art method for exposing the peripheral part of the wafer is to conduct a circumferential exposure of a peripheral region with a fixed width from an edge of the wafer.
However, there is a demand that a wafer can be utilized to the utmost extent bringing about no reduction in yield, in view of an efficiency of utilization of the wafer, or utilize to the entire extent other than several wafer portions at which the wafer is held by holding claws.
Accordingly, a technique for selectively exposing only portions contacting with the wafer-holding claws is required
However, it is technically very difficult to selectively expose a predetermined are on the peripheral part which is assigned as a region contacting with the wafer holding claws.